• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.116-116
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• 2011

AZ31과 AZ80의 마그네슘합금 소재를 이용하여 분극곡선과 전기화학적 임피던스를 측정하였고, 다른 금속과 접촉하여 대기환경에 노출시킨 부식시험을 하였다. 그 결과 AZ31보다는 AZ80의 부식저항이 더 큰 것을 확인할 수 있었고, 마그네슘 모재가 이종금속과 접촉된 상황에서 Cu>Fe>Al의 접촉재 순으로 부식이 진행되었다.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.32-32
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• 2009

실리콘 박막 태양전지에서 전면 투명전도막(TCO)은 태양전지의 전기, 광학적 특성을 결정하는 중요한 기능을 한다. ZnO:Al TCO는 기존에 사용되던 $SnO_2:F$와는 비정질 실리콘(a-Si:H) 박막 태양전지의 윈도우 층으로 사용되는 p a-SiC:H와의 일함수(work function) 차이로 인해 접촉전위(contact barrier)를 형성하게 되며 이로 인해 태양전지의 충진율(fill factor)이 $SnO_2:F$에 비해 감소하는 단점을 보인다. 본 연구에서는 ZnO:Al/p a-SiC:H 계면의 접촉전위 발생원인 및 태양전지 충진율 감소현상에 관한 정확한 원인규명을 위해 다양한 특성을 갖는 버퍼층을 삽입하여 계면특성 및 태양전지의 동작특성을 분석하고자 한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.273-273
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• 2012

최근 스마트 윈도우, 자가세정(Self-Cleaning), 김서림방지(Anti-Fogging), 디스플레이 표시장치, 대전방지 코팅 등 다각적으로 활용이 가능한 PTFE (Ploytetrafluoroethylene)를 Sol-gel, Sputtering, Spin-Coating, CVD (Chemical vapor deposition)방법을 이용하여 낮은 표면에너지와 나노사이즈의 표면 거칠기를 가지는 $150^{\circ}$ 이상의 초-발수성 표면에 대한 많은 연구가 진행되고 있다. 본 실험에서는 영구자석을 이용한 고밀도 플라즈마로 높은 점착성과, 균일한 박막 및 대 면적 공정이 가능한 RF-magnetron sputtering방법을 이용하여 Plasma etching으로 표면적의 거칠기와 낮은 표면에너지를 만든 뒤, 발수특성을 가진 PTFE를 증착하여 접촉각 변화와 구조적 및 광학적 특성을 측정하였다. AFM (Atomic Force Microscope)측정결과 100 w에서 가장 높은 1.7 nm의 RMS(Root mean square)값이 측정되었고, 접촉각 측정결과 Plasma etched glass는 25 w에서 125 w로 증가함에 따라 친수성을 나타내었으며, 100 w에서 가장 낮은 $15^{\circ}$의 접촉각을 나타내었다. PTFE박막을 증착하였을 때는 100 w에서 $150^{\circ}$의 초발수 특성을 나타내었고, 투과율 측정 결과 85%이상의 높은 투과율을 나타내었다. Plasma etching을 이용한 PTFE 발수 특성은 비가 오면 자동으로 이물질이 씻겨 내리는 자동차 유리등의 개발이 가능하고, 높은 투과율이 요구되는 액정표시장치(LCD)같은 차세대 대형 디스플레이의 표면 코팅에 사용이 가능 할 것이라 사료된다. 본 연구는 중소기업청에서 지원하는 2011년도 산학연 공동기술개발 지원사업의 연구수행으로 인한 결과물임을 밝힙니다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.358-359
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• 2012

최근 분극 특성이 상이한 무분극 GaN 에피성장에 관한 심도 있는 연구와 함께 전자-전공 캐리어의 주입 및 캐리어의 거동, 방출되는 편광 특성 및 다양한 물리적 특성들에 대해 보고되고 있으며, 광학적 특성 및 물리적 특성의 확보를 위한 많은 연구가 활발히 진행 중이다 [1]. GaN의 ohmic 접촉(ohmic contact)의 형성은 발광 다이오드(light emitting diode), 레이저 다이오드(Laser), 태양전지(solar cell)와 같은 고신뢰도, 고효율 광전자 소자를 제조하기 위해서는 매우 중요하다 [2]. 그러나 이와 함께 병행 되어야 할 무분극 p-GaN 의 ohmic contact에 관한 연구는 많이 이루어지고 있지 않는 실정이다. 따라서 본 논문에서는 r-plane 사파이어 기판 상에 성장된 p-GaN에서의 ohmic 접촉 형성 연구를 위하여 Ni/Au ohmic 전극의 접촉저항 특성을 연구하였다. 본 실험에서는 성장된 a-plane GaN의 Hole농도가 $3.09{\times}1017cm3$ 인 시편을 사용하였다. E-beam evaporation 장비를 이용하여 Ni/Au를 각각 20 nm 그리고80 nm 증착 하였으며 비접촉저항을 측정하기 위해 Circle-Transfer Length Method (C-TLM) 패턴을 사용하였다. 샘플은 RTA (Rapid Thermal Annealing)를 사용하여 $300^{\circ}C$에서 $700^{\circ}C$까지 온도를 변화시키며 전기적 특성을 비교하여 그림 1(a) 나타내었다. 그림에서 알 수 있듯이 $400^{\circ}C$에서 가장 낮은 비접촉저항 값인 $6.95{\times}10-3{\Omega}cm2$를 얻을 수 있음을 발견하였다. 이 때의 I-V curve 도 그림1(b)에 나타낸 바와 같이 열처리에 의해 크게 향상됨을 알 수 있다. 그러나, $500^{\circ}C$ 이상 온도를 증가시키면 다시 비접촉 저항이 증가하는 것을 관찰하였다. XRD (x-Ray Diffraction) 분석을 통하여 $400^{\circ}C$ 이상열처리 온도가 증가하면 금속 표면에 $NiO_2$가 형성되며, 이에 따라 오믹특성이 저하 된다고 사료된다. 또한 $Ni_3N$의 존재를 확인 하였으며 이는 nonpolar surface의 특성으로 인해 nitrogen out diffusion 현상이 동시에 발생하여 계면에는 dopant로 작용하는 질소 공공을 남기고 표면에 $Ni_3N$을 형성하여 ohmic contact의 특성이 저하되기 때문인 것으로 사료된다.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.40-46
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• 2011

In the field application of the conventional acoustic nonlinear technique using through transmission of bulk waves to evaluate the contact acoustic nonlinearity(CAN) in solid-solid contact interfaces like as in the closed crack, it has difficulty to access inner position for attaching the pulsing or receiving transducer. In the present study, a new reflection technique has been suggested to measure the acoustic nonlinearity in solid-solid contact interfaces, which uses both of pulsing and receiving transducers on the same side of target and so that it will be very useful for the field application. For this, based on the linear and the nonlinear contact stiffness estimated by the power-model of the contacting pressure, the nonlinear parameter of the reflected ultrasonic wave at the interfaces has been theoretically calculated. Experimental results in contact interfaces of A1606l-T6 alloy specimens with loading pressure showed good agreement with the theoretical predictions, which proves the validity of the suggested reflection mode technique.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.69-75
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• 2008

Shear tests were carried out on interface between two concrete eco-blocks which comprise segmental retaining wall. Three interface conditions were considered : 1) direct contact of two blocks, 2) placing rubber pad between two blocks, 3) placing rubber pad and shear key between two blocks. According to shear tests, shear load-shear displacement relationship which was obtained from direct contact of two blocks was similar to elastic-perfectly plastic behavior. Ductile behavior of shear load-shear displacement relationship was observed for the interface condition of placing rubber pad. Apparent minimum shear capacities and apparent friction angles for the interface conditions of direct contact of two blocks, placing rubber pad between two blocks, placing rubber pad and shear key were 1.7 kN/m, $27.6^{\circ}$ and 4.2 kN/m, $26.2^{\circ}$ and 20.9 kN/m, $26.0^{\circ}$ respectively.

• Journal of the Korean Vacuum Society
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• v.11 no.4
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• pp.201-206
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• 2002

Pd/Si/Pd/Ti/Au ohmic contact to n-type InGaAs was investigated with rapid thermal annealing conditions. Minimum specific contact resistivity of $3.9\times10^{-7}\Omega\textrm{cm}^2$ was achieved at $400^{\circ}C$/20sec. This was related to the formation of Pd-Si compounds by rapid thermal annealing and the in-diffusion of Si atoms to InGaAs surface. However, the specific contact resistivity increased slightly to low-$10^{-6}\Omega \textrm{cm}^2$ at $400^{\circ}C$ for longer than 30 seconds, and to high-$10^{-7}$ at 425~$450^{\circ}C$ for 10 seconds. This resulted from the formation of Pd-Ga compounds. Superior ohmic contact and non-spiking planar interface between ohmic materials and InGaAs were maintained after annealing at high temperature. Therefore, this thermally stable ohmic contact system is a promising candidate for compound semiconductor devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.12
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• pp.1627-1633
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• 2011

Injection molds are generally fabricated by assembling a number of plates in which the core and cavity components are assembled. This assembled structure has a number of contact interfaces where the heat transfer characteristics are affected by thermal contact resistance. In previous studies, numerical approaches were investigated to predict the effect of thermal contact resistance on the temperature distribution of injection molds. In this study, thermal-fluid coupled numerical analyses are performed to take into account the thermal contact effect on the numerical evaluation of the mold filling characteristics. Comparisons with experimental results show that the proposed coupled analysis provides more reliable results than the conventional analyses in predicting the mold filling characteristics by taking into account the effect of thermal contact resistance inside the injection mold assembly.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.249-263
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• 2017

The expansion behavior of inflatable steel pipe rockbolt shows geometric nonlinearity due to its ${\Omega}-shaped$ section. Previous studies on the anchoring behavior of inflatable steel pipe rockbolt were mainly performed using theoretical method. However, those studies oversimplified the actual behavior by assuming isotropic expansion of inflatable steel pipe rockbolt. In this study, the anchoring behavior of the inflatable steel pipe rockbolt were investigated by the numerical method considering the irregularity of pipe expansion and other influencing factors. The expansion of inflatable steel pipe rockbolt, the contact stress distribution and the change of the average contact stress and the contact area during installation were analyzed. The contact stresses were developed differently depending on the constitutive behavior of rocks. Small contact stresses occurred in steel pipes installed in elasto-plastic rock compared to steel pipes installed in elastic rock. Also, the anchoring behaviors of the inflatable steel pipe rockbolt were different according to the stiffness of the rock. The steel pipe was completely unfolded in the case of the stiffness smaller than 0.5 GPa, but it was not fully unfolded in the case of the stiffness larger than 0.5 GPa for the given analysis condition. When the steel pipe is completely unfolded, the contact stress increases as the rock stiffness increases. However, the contact stress decreases as the rock stiffness increases when the steel pipe is not fully expanded.

• Journal of Korea Water Resources Association
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• v.35 no.2
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• pp.221-229
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• 2002

For the efficient design of baffled Powdered activated carbon(PAC) contractor, which has been widely used in water treatment plant(WTP) against the algae-related odor problems, a CFD(computational fluid dynamics) program was applied. In order to verify the performance of FLOW-3D program, the previously reported results of tracer tests from a pilot-scale PAC contractor(working volume of 288 liters) were compared to those from FLOW 3D. The results of FLOW-3D simulation were very similar to those from tracer tests conducted with the Pilot-scale PAC contactor. On the other hand, the hydrodynamic characteristics of baffled contractor in the P-WTP were simulated by using FLOW-3D. Simulation results on the distribution of PAC particles showed that there are some stagnant parts in the back side of baffles in which PAC Particles are not present. These stagnant parts might decrease the adsorption capacity of PAC particles. When the baffles were changed to maze-type intra-basin baffling, PAC particles were evenly distributed and the amount of stagnant parts reduced. In conclusion, it is anticipated that FLOW-3D simulation could be a viab1e tool for analyzing the hydrodynamic characteristics of structures used in drinking water treatment plant.